Both sides of the body need to function well to play good golf. The better the
sides coordinate, the better you'll hit it. The weak side of the body must be dominant from set-up to just before impact. These left side exercises are a must for anyone wanting to excel. In addition to these exercises, practice teeing the ball with the left hand, putt with the left arm-only, etc. In other words, get the left involved.
The left arm dominates the swinging of the club from set-up to a point 1/2 way into the downswing. A good, strong left hand grip is required but the left arm must also be exercised.
If you've got the basic Y Shape idea with the club remaining in front of the body thru the ball, go ahead and pull the grip end way down past your waist. It feels like the clubhead will never catch up with the hands at impact. Then just turn thru...
Resist the tendency to aim the clubhead at the ball, resulting in a mis-hits at impact. When you 'aim' you push the clubhead vertically down before impact. Work the shaft around the body and let the clubhead drop down on its own.
Both sides of the body need to be practiced and exercised. The right applies power but the left must continue to pull as far thru the ball as possible to maintain the Y Structure.
Video is kinda fuzzy but this one details how to firm up thru the ball, good for all kinds of short shots. Good for inside practice with soft balls.
Prelude to a full left arm-only swing. Go from position to position until it feels like a smooth, one piece swing. Keep the 90º angle!! Then add the right hand but always keep the 90º angle in mind. Good inside practice; do this one a lot.